Many factors can potentially influence the ability of exotic species to invadenative communities (invasibility) and the susceptibility of native communities to theimpacts of invading species (vulnerability). Existing models on these subjects havegenerally not considered spatial components and stochasticity associated with invasionevents. We used spatial stochastic modeling to examine the interaction of habitat configuration and disturbance with demographic characteristics of invading plant species on invasibility and vulnerability of plant communities. For spatial structure we used simulated stream networks that varied in complexity as the spatial organization of these systems determines the distribution and extent of habitats, and their interconnectivity influences how species access resources. A factorial design that included two networks configurations of varying spatial complexity, and two distinct levels each of four invading species traits (age to reproduction, reproductive rate, competitive ability and dispersal range), suggest that highly dendritic networks were more susceptible to invasion and the entire suite of demographic traits were important for predicting invasibility. However, habitat structure is not static especially in dynamic and heterogeneous stream systems. To explore the dynamic relationship between habitat structure and life history traits we expanded the factorial design to include disturbance and invasive species propagule pressure.
Results/Conclusions
Increasing propagule pressure (introduction frequency) always had a positive effect on invader abundance, but increasing disturbance frequency reduced invader abundance with low propagule pressure, and increased invader abundance at the intermediate and high intensities of propagule pressure. Disturbance in the mid portions of the network increased invader abundance in both network configurations whereas disturbance at the base or in low order streams reduced invader abundance particularly in the less complex network. Support for this model from empirical studies may aid in the future development of management strategies for watersheds dealing with riparian invasion issues.
